Apparatus for forming plaster-keying depressions in plasterboard



Aug. 16, 1949. G. A. BUTTREss y FOR FORMING PLASTER-KEYING APPARATUS DEPRESSIONS IN PLASTERBOARD Filed May 11, 194e Patented ug. 16,n 1949 APPARATUS FOR FORMING PLASTER-KEY- ING DEPRESSIONS IN PLASTERBOARD George A. Buttress, Los Angeles, Calif. Application May 11, 1946, serial No. 669,185

3 Claims.

This invention relates to the production of plaster board of the type shown in my pending application for patent, Serial No. 654,151, filed March 13, 1946, and more particularly pertains to and has for its primary object the provision of a novel apparatus for forming in plaster board before theplastic ller or body thereof has set and while the cardboard or other paper cover sheets of the board are still wet, a plurality of depressions which are shaped and dimensioned to provide for a reliable keyingV and bonding to the board of the plaster which applied thereover as when the board is mounted upon a wall or ceiling.

One of the objects of the present invention is to provide a novel depression-forming tool which is subject to use in gangs and Aconstructed and arranged to that when forcibly pressed Yagainst one of the cover sheets of a plaster board in the condition above noted, will'iirst shear from the cover sheet proper a strip portion without severing the ends'of said strip portion from the sheet and then depress the strip portion and displace the soft plastic filler to form a depression which has its bottom arched and covered by said strip portion whereby there will be provided reinforcing factors which will compensate for the Weakening effect of the depression.

Another object is to provide an expansible depression-forming tool which is constructed and arranged so that in response to pressure applied thereto in the operation of forming a depression and because of the resistance to further inward movement of the tool which is set up when the plastic material in the depression zone is Vfully compressed, it will expand and give-the depres-V sion a formation in cross section whereby plastic applied to the board will be effectively keyed thereon.

Another object is to provide a selfexpanding depression-forming tool such asY described which is of simple and inexpensive construction, con-k sists of comparatively few parts and is subject to ruse in gangs with a likewise simple form of apparatus for pressing the tools into and Withdrawing them from the plaster board.

With the foregoing objectsrin view, together apparatus embodying the present invention show-IY ing'a gang of the depression-forming tools positioned in readiness for operation on a strip or sheet of plaster board,

Fig. 2 is a sectional View taken on the line 2-2 of Fig. 1, but showing how each tool is initi-V ally pressed into the plaster board when a depression is partly formed,

Fig. 3 is a sectional View of the parts as shown in FigA 2, taken at right angles to Fig. 2, showing the tool as it appears when the depression is in the stage shown in Fig. 2,

Fig. 4 is a sectional view similar to Fig. 3 showing how the tool is automatically expanded to give the depression a dovetail formation in cross sectionv and finish the formation of the Ydepression,

Fig, 5 is an enlarged sectional View taken on the line 5-5 of Fig. 2 showing how the tool-supporting plate pressed against the tool in forcing it into the plastic board, and

Fig. 6 is a fragmentary perspective view of a portion of a finished plaster board as produced with the apparatus hereof.

Referring to the drawing more specically it will be seen that one form of apparatus embodying this invention generally includes a plurality of the depression forming tools A hereof'mounted on a suitable supporting plate B for simultaneous application to a sheet of plaster board C supported on a table D or the like. Any suitable means not shown may be connected to the plate B for example, by means of the rod E, for moving the support B whereby the tools A may be applied to and removed from the plaster board for forming depressions therein in accordance with this invention.

Each of the tools A as here provided is constructed and arranged to produce an elongated depression with the bottom'thereof given a double arch formation and lined by a strip F of the uppermost of the cardboard cover sheets G, to lend strength to the board and cover the plastic filler or body H which would otherwise -be exposed `in the finished board and absorb moisture from freshly applied plaster. The double arch formation is produced by the bottom of the depression being generally of concave form longitudinally in the depressions zones is encountered. Tov this' end each of the tools is of sectional form with the sections spring-loaded to remain in close association with one another during the stages of the depression forming operation preliminary to encountering the resistance of the fully compressed plastic body at the depression zones as aforesaid, at which time they will expand and swing outwardly and widen the bottoms of the depressions in a dovetail formation. This action is assured by giving the working `faces of the movable die sections an inclination and shape productive of a cam action against the particularly shaped bottoms of the depressions.

The tool-supporting plate B is made in two plate-like sections 'I and B provided with vertical tool-receiving openings 9 and formed with complementary grooves II) in their opposed faces. Rods such as the one I I here shown are mounted in the grooves I as a means for pivotally supporting rows of the tools with the latter projecting below the plane of the plate an extent substantially equal to the depth given the depressions formed when the tools are pressed into the board C while in a state in which the cardboard coversheets G are wet-and before the plastic body H has set.

As here provided each of the tools A comprises a pair of shoe-like die members I2 of identical formation-adapted to be depressed into the plaster board. These die members are carried on the lower ends of like upright Shanks I4 so that each die member and its associated shank forms an inverte-d T-shaped `part of the sectional tool with the head of said part constituting the die member. As here shown the shanks Id are rectangular have their Wideriaces opposed and are provided intermediate their ends with registering but angularly related transverse openings i5 through which openings the rod I `I is extended to loosely pivotally support the tool `in its associated opening- 9 in the plate B. Fig. 3 shows how the openings I5 4in the shanks I 4 in having their axes inclined from the horizontal -will accommodate the rod I I so that the Shanks are capable of limited pivotal or rocking movement when Ythe tool is expanded and the die members are spread apart. It should be noted that the upper lids It of the shanks Irl iit snugly against opposite sides of the associated opening 9 -in the plate B and that below the pivot` rod I I,'the opening 9 is enlarged as at 9 to permit the Shanks to be swung apart as aforesaid.

The Shanks I4 are reduced in thickness as at I4' from the points where the openings Yl5 are formed to their outer ends, so as to be spaced apart, while vthe portions of the shanks extending from said openings to the inner or lower ends thereof abut one another and have rounded fulcrum portion I4" adjacent said opening. Fig. 4 shows how -the portion I4" coact when the die members are spread apart.

An expansion spring I8 is mounted in sockets I9 in opposed faces of the upper ends Ill' of the Shanks I4 to hold the die members I2 in opposed abutting relation as a unit for forming a single depression when pressed into the plaster board as shown in Figs. 2 andf3.

Each of the die members I2 is shaped as a segment of a circle, having a longitudinally convex or curved `depression-forming lower face I2 and a transversely inclined upper face 2. The lower face I2 'is also transversely inclined in the same manner as the upper face. Thus the plaster board contacting :face of the tool as provided by the lower faces of the two die members I2 when in abutting relation as shown in Figs. 3 and 5, is concave transversely and of an inverted V- 4 shape, whereas the upper faces I2 are convex transversely and of a similar inverted V-shape in cross section. Fig. 5 shows how the proximate side edges of the upper faces I2" form apical bearing portions in contact with the under side of the plate B. This arrangement provides for a direct pressure from the plate B onto the die members without depending upon the pivot rod 'I I. Thus the pivotal mountings of the Shanks I4 are 'free of the load applied when the plate is operated to press the tools into the plaster board. The inclined faces I'2 extend divergently relative to plate B from the points Where the proximate edges of said faces contact said plate, thereby providing a clearance as shown in Fig. r-5 which make possible the spreading `apart of die members I2 in arcuate paths into 'the position shown in Fig. 4.

The outer sides of the die members are somewhat inwardly inclined :towards the upper faces I2, so that in the final depression forming operation the depression will be given a dovetail cross section.

@partition Upon depressing therplate B from position over the plaster board C as shown in Fig. l, the tools A will be pressed into the Vboard and form the depression as indicated in Figs. 2 and 3.

As each tool is pressed against the board it will depress into the `board while displacing the soft plastic ,ller, "a vstrip portion F of the upper cardboard cover sheet G. As this operation takes place while the plastic ller is soft and the cover sheets are wet, thestrip portion will be depressed without having .its `ends torn or severed from the cover sheet proper. The outer edges of the depression forming vfaces |12 on the dies I 2 in being convex will have a progressive shearing action on the cover sheet as the tool is being depressed and this prevents the paper `from being torn except along said edges also .causes small flange portions of the Vpaper to be .pressed into the depression and lie against opposite sides -of the depression as best shown in Fig. 5.

When each tool has been pressed into the board the extent shown in Figs. 2 and 3, the plastic material beneath vthe depressed strip portion F and the bottom cover .sheet G will be compressed and increased in densi-ty as indicated at K and. the bottom of the depression will be given the shape of the combined faces I2' yof the dies I2. This provides the vbottom with a ridge L along its longitudinal medial line and this ridge is sloped on inclined downwardly opposite sides towards the side walls of the depression. As the downward pressure is appliedon each .tool A, the faces I2 in being transversely inclined and lying in parallelism to the inclined side faces or" the ridge L, will have a cam action vdownwardly and outwardly and cause the die members to spread apart. This cam action is caused by the added resistance to further inward movement of the tool as developed .bythe compressed plaster material indicated at K. However, the tool is somewhat further depressed and deepens the depression while the die rmembers spread apart. Due to this spreading apart of the die members I2 in arcuate paths the outer sides of said members will displace the plastic ller and produce inclined side walls in the depression such that the depression is given a dovetailed formation in cross section.

When the plate B is raised, the tools will be lifted andthe die .members I2 will `be forced back s in abutting relation by the being withdrawn. d

It will now be seen that by means of the depression forming tool and associated apparatus as here provided, it is possible to quickly and inexpensively produce a plurality of keying depressions in a strip or sheet of plaster board with one op eration of a simple apparatus and with the depressions serving to reliably bond and hold plaster on the board.

While I have shown and described a specific embodiment of my invention, I do not limit myself to the exact details of construction set forth, and the invention embraces such changes, modifications and equivalents of the parts and their formation and arrangement as come within the purview of the appended claims.

I claim:

1. In apparatus for forming plaster-keying depressions in plaster board of the paper covered plastic filled type at the stage of manufacture before the paper covering has dried and before the plastic ller has set, a depression forming tool, a support for said tool affording the movement of the tool into and out of depression forming position, said tool including complementary die members, shanks on said die members, means loosely pivotally mounting said Shanks on said support so that said die members may be swung apart and swung back into closely associated relation, spring means holding said die members together for operation as a unit to make a single depression, said die members having oppositely inclined surfaces opposed to said support and arranged so that only the proximate edge portions of said surfaces will contact said support whereby the depression-forming pressure is directly applied by said support to said die members at said edges and said inclined surfaces provide a clearance permitting the die members to be spread apart in arcuate paths, and surfaces on said die members constructed and arranged so that after a depression is formed and upon continued pressure on said members by said contact thereof with said support, said surfaces will have a cam action against the bottom of thedepression and spread the die members apart and widen the depression.

2. In apparatus for forming plaster-keying depressions in plaster board of the paper covered plastic lled type at the stage of manufacture before the paper covering has dried and before the plastic filler has set, a depression forming tool, a support for said tool affording the movement of the tool into and out of depression forming position, said tool including complementary die members, shanks on said die members, means loosely -pivotally mounting said shanks on said support so that said die members may be swung apart and swung back into closely associated relation, spring means holding said die members together for operation as a unit to make a single depression, said die members having oppositely inclined surfaces spring f8 as they are 6 A opposed to said support and arranged so that only the proximate edge portions of said surfaces will contact said support whereby the depressionforming pressure is directly applied by said support to said die members at said edges and said inclined surfaces provide a clearance permitting the die members to be spread apart in arcuate paths, and surfaces on said die members constructed and arranged so that after a depression is formed and upon continued pressure on said members by said Contact thereof with said support, said surfaces will have a cam action against the bottom of the depression and spread the die members apart and widen the depression, said die members having side surfaces shaped so as to form the depression with inclined side walls and provide a dovetail formation therein.

3. In apparatus for forming plaster-keying depressions in plaster board of the paper covered plastic lled type at a time when the paper is wet and before the plastic filler has set, a plate-like support subject to movement towards and away from a supported strip of such plaster board and having a plurality of openings therein, a plurality of depression-forming tools mounted in said openings for movement with said support to form depressions in said board, each of said tools including a pair of opposed complementary depression-forming die members, upstanding shanks supporting said die members and extending into one of the openings in said support, a pivot pin loosely pivoting said Shanks at a point between their ends to said support, a spring interposed between the upper ends of said shanks for yieldably holding said die members close together for making a single depression upon being pressed into said plaster board, portions of the Shanks between the pivots and said die members abutting and serving as fulcrum points, said die members having their upper surfaces oppositely inclined so REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 373,572 Van Winkle Nov. 22, 1887 669,913 Dalton Mar. 12, 1901 Marlow Aug. 8, 1905 

